Estrogen receptor levels in hypothalamic and vocal control nuclei in the male zebra finch.

Estrogens play an important role in the activation and differentiation of vocal behavior in male zebra finches. In the present experiment, we conducted a series of in vitro binding assays to quantify estrogen receptor concentrations in individual hypothalamic and vocal control nuclei. Receptor concentrations were measured in cytosol fractions obtained from castrated males and, since adrenalectomy is not a viable possibility in this species, in castrated males treated with 1,4,6-androstatriene-3,17-dione (ATD), an inhibitor of estrogen synthesis. Specific, high-affinity estrogen binding was detected in both untreated castrates and castrates treated with ATD. Although ATD treatment had no effect on estrogen receptors in hypothalamic-preoptic tissue, ATD-treated males had significantly higher levels of [3H]estrogen binding in 3 vocal control nuclei: the dorsomedial portion of the intercollicular nucleus (DM), the magnocellular nucleus of the anterior neostriatum (MAN), and Area X. Low levels of estrogen binding were also detected in cytosol from the caudal portions of the ventral hyperstriatum (HVc) and the robust nucleus of the archistriatum (RA) of both untreated and ATD-treated castrates. In most brain regions examined, estrogen receptor levels were lower than androgen receptor levels measured in previous experiments. The presence of both androgen- and estrogen-concentrating neurons in these areas provides compelling evidence for the interaction of androgens and estrogens in the neural control of male vocal behavior in this species.